Ribbon type resistor



Jul 10, 1962 R. VRADENBURGH ETAL 3,044,034

RIBBON TYPE RESISTOR Filed Dec. 21, 1960 oll 44 48 4b 40 2Q n i INVENTORS (056 1- K9400101 6 By Ayn up Cuwro/v Sqlemq i I & 'Lb k/jgnmf H. Havew Z A 25 T i aw Unite States Patent 9 3,044,034 RIBBON TYPE RESISTOR Robert Vradenburgh, Yonkers, N.Y., Arthur Clayton This invention relates to resistive devices, particularly to resistive devices of the metal ribbon type.

Metal resistors having a high wattage are made from thin,-high resistance metal ribbon. The ribbon is formed in flat spaced loops to permit circulation of air and dissipation of heat. It is preferable to support the loops at the centers. However, with large loops it has been necessary in order to secure the required stiffness to support the loops at theends. This latter form of supporting the ribbon is not as desirable as supporting the ribbon at the center of the loops. The end supported resistors are more expensive and have less heat dissipation than similar center supported resistors. Therefore, the center supporting of the metal ribbon is preferred. The present metal ribbon resistors formed in large loops and supported at the center of the loops distort under heat causing the loops to short, and if a cooling medium is forced across the resistors the circulating currents will causethe loops to vibrate and fracture.

An object of the invention is to increase the wattage dissipation of metal ribbon type resistors that are formed in loops and supported at the center of the loops.

Another object of the invention is to increase the overall rigidity and the firmness of the mounting of metal ribbon resistors formed in loops.

Another :object of the invention is to increase the resistance and wattage dissipation of metal ribbon type resistors without substantially increasing the cost of manufacture.

Other and further objects and advantages will be apparent from the following description taken in connection with the drawings, in which FIG. 1 is a side view of the resistive device;

FIG. 2 is an end view of the resistive device;

FIG. 3 is a side view of the resistive ribbon before being formed into loops; 7

FIG. 4 is a cross sectional view of the resistive ribbon and mounting taken along lines 4-4 of FIG. 1;

FIGS. 5, 6 and 7 are sectional views of various embodiments of the ribbon at a section similar to section AA of FIG. 1;

FIG. 8 is an exploded view of the ribbon mounting means;

FIG. 9 is'a perspective view of another embodiment of the clamp; and

FIG. 10 is a side view of the embodiment of the clamp shown in FIG. 9.

Referring to'FIG. 1, the resistive metal ribbon 19 is secured'to a mounting strip 11 by fastening means 12. The ribbon has terminals 14a, 1412 at opposite ends of the ribbon for passing current through the ribbon. The resistive ribbon is formed as a continuous piece with long sections 13 having a generally U shape in cross section with intervening flat portions 15. The ribbon is bent into a plurality of flat tops with the sections 13straight and Patented July 10, 1962 the fiat portions 15 forming the curved parts or ends of the loop. The straight sections 13a, 13b of the loops are at an angle to the strip 11 with the sections 13a at an angle to the sections 13b. The metal ribbon is mounted on the insulating strip 11 by the clamping means 19. a

The insulating strip 11 may be made of any suitable material. A plurality of evenly spaced holes 20 are provided along the strip. The holes extend through the strip from one side 21 to the other side 22. The clamping means comprises a bolt 23, a nut 24 and a clamp 25. The bolt is of a conventional type with a head 26 and a threaded portion 27 on which the nut is threaded. The clamp 25 has generally the cross sectional shape of a double U. The clamp 25 is formed as a single piece with two spaced sides 30, 31 extending in spaced parallel planes. The sides are connected by an inverted center U portion 33. The center portion comprises a panel 34 and two side legs or portions 35, 36 extending parallel to the sides 34), 31 and connected thereto by rounded edges 37, 38. The clamp forms a rigid member. The sides 30, 31 filrnly support the ribbon on the strip.

The center panel 34 has a cylindrical opening or hole 39. The hole is formed with a boss 44) on the underside 42 of the panel 34. The hole is tapped to receive the threaded shaft 27. The boss 40 provides extra length to the hole and rigidity to the panel so that on tightening of the bolt '23 the edges of the clamp become firmly embedded in the insulating strip. The rigidity of the clamp permits 'a firm stressing of the clamp to hold it in place. The embedded edges and the threaded opening form with the bolt an anti-turn means.

When the clamp is in position a passage 44 is formed by the center portion 33 and the insulating strip 11. This passage provides for the flow of air along the underside 42. This aids in the conduction of and dissipation of heat from the clamp and reduces the transference of heat to the strip. I

The resistor ribbon engages the upper side 43 of the center panel 34. The parallel side legs and sides are also spaced to form passages 45, 46 which aid in the removal of heat by permitting the passage of air along the outer surfaces 47, 48 of the portion 33. The passages prevent the clamp from overheating and thus prevent the loosening of the clamping means due to expansion and contraction.

The resistive ribbon 10 is fastened to the clamp by means of a lock washer 28 and nut 24. Each section has a hole 29. The bolt 23 passes through the hole 29 in the ribbon. The Washer 28 is between the nut and the ribbon. Thus with the tightening of the nuts the ribbon is securely fastened to the insulating strip.

In FIGS. 9 and 10 a modification is illustrated in which the sides and center portion are the same. The edges bearing against the insulating strip have projections 49 extending away from the clamp. The projections are triangular in shape and are formed at the time the clamp is made by extending the sides 30, 31, 35, 36 at the corners. These projections provide additional means to prevent the turning of the clamp.

The thin metal ribbon is illustrated in four embodiments 10, 10a, 10b, and of FIGS. 4, 5, 6 and 7 respectively. In each of these embodiments the ribbon has a generally U shape with sides substantially at right angles to the center. The center is preferably planar and has 7 holes for fitting the ribbon over the mounting bolt 23.

The center bears against the center panel 34 of the clamp. The metal ribbon is supported freely in the cooling medium only engaging another structural member at the clamping means.

The preferred form is illustrated in FIG. 4 in which the sides 50', 51 have curved edges 54, 55 extending from the center 52 and turning to extend the sides generally normal to the center. The center may be referred to as a longitudinally extending member. The sides have inwardly extending channels 56, 57 and straight portions. The straight portions 58, 59 provide an outward flare to the open end of the ribbon. This structure provides the combination of a channel shape formed by the sides 50, 51 and the center 52 with each side having a channel to form a triple channel member. This provides for a substantial reduction in the thickness of the ribbon With an increase in rigidity or stiffness. The ribbon does not bend under the variations in temperature and the forced circulation of cooling air.

The modifications illustrated in FIGS. 5 and 6 have center panels 52a, 52b respectively, with sides 50a, 51a and 50b, 51b extending normal to the center to form a longitudinally extending channel 78 in each embodiment. The sides 50a, 51a have inner beads or channels 60, 61 extending vlongitudinally forming with the channel 73 a triple channeling of the strip. The beads 60, 61 are spaced from the center 52a and from the free edges of the sides. The longitudinal beads or channels 62, 63 of FIG. 6 extend outwardly and are spaced from a respective free edge and the center 52b. Thus each side comprises an intermediate channel with flat portions on each side thereof. 7

In the embodiment of FIG. 7 the sides 50c, and-51c have longitudinally and outwardly extending beads or channels 64, 65. The flat portion between the bead and the center is substantially normal to the center 520. The edge portions 580, 59c flare outwardly from a position normal to the center 52c. It is thus seen that these additional embodiments have the multiple or triple channeling which stiifens the metal ribbon so that it may withstand increased heat and vibration.

The metal ribbon is formed into flat, narrow loops with the stiif sections 13a and 13b forming the straight sides of the loops and the flat portions 12 forming sharply curved ends. The sections 1311 are spaced in parallel relation forming spaces 75 between the sections. The sections 13b are in spaced parallel relation forming spaces 76 between the sections. Each set of straight sections of side 13:: and 13b are aligned in a respective plane. The sets are spaced apart to form a passage 77 between the sections. The spaces 75 and 76 are parallel to the channel 78 formed by the sides 50, Sland the center 52.

The insulating strip 11 extends through the passage 77 parallel to the sections and adjacent to the midpoint thereof. The sections are individually fastened at their midpoints to the insulating strip by the clamping means 19. The clamping means firmly holds the sections 13a, 13b in the proper parallel relation with the curved ends free and spaces the sections from the strip 11. The sections contact only the clamping means and, as previously described, the clamp 25 spaces the panel 34 which directly supports the metal ribbon from the insulating strip and provides a circulating passage 44 between the panel 34 and the strip 11. Thus the flat sides of the loops are stiff and supported free of other structural members so that a cooling medium, such as air, may be forced against the sections and through the clamping means to remove the heat from the resistor and increase its heat dissipation capabilties.

The spacing of the center 52 of the ribbon separates the'ribbon from the insulating strip and reduces the heat transfer to the insulating strip. The passage 44 by the circulation of air therethrough also reduces the heat transfer to the insulating strip. The strip therefore has a greater dimensional stability and retains the clamp firmly in place. The clamping means does not shift or loosen and the sections 13a and 13b are securely held in the proper parallel relationship under severe vibration and temperature changes.

The increase in stiffness of the sections and the firmness of the mounting permits longer sections of thin higher unit resistance ribbon that can withstand the turbulence of the forced circulation cooling the ribbon and the excess vibration.

The resistor is made of only a few parts and is easily assembled. The clamps 25 are threaded on the bolts 23 passing through the holes 26 in the strip. The metal ribbon is shaped and formed in loops by machinery and each section mounted on a single clamp by the washer and nut. Thus the cost of manufacturing is comparable to the lower wattage resistors.

From the foregoing description it is thus seen that a new high wattage metal ribbon type resistor, capable of withstanding the strains produced by heat and vibration, has been provided at low manufacturing costs. The invention is set forth in the appended claims.

We claim:

1. A resistor of the ribbon type comprising a mounting strip having surfaces on opposite sides, a plurality of clamps each having spaced parallel sides extending normal to the strip and an inverted U-shaped member having a center panel with side portions, said center panel positioned between said sides and said side portions connecting said center panel with said sides to space said panel from said strip to form a forced circulation passage between said center panel and said strip, fastening means extending through said center panel and said strip from one side to the other to forcefully draw said sides against said insulating strip to prevent twisting of said clamp, a resistor ribbon formed in a plurality of aligned loops with parallel first sections fastened to said clamping means in planar alignment, curved parts successively connecting sections on alternate sides to form a continuous resistive ribbon, said sections comprising an intermediate longitudinally extending member and two sides extending generally normal to said member from opposite longitudinal edges, said sides having longitudinally extending channels cooperating with the channel formed by said sides and intermediate member to stiffly retain said sections in spaced relation to adjacent sections under conditions of forced circulation and vibration.

2. A resistor as set forth in claim 1 wherein said side channels are formed inwardly.

3. A resistor as set forth in claim 1 wherein said side channels are formed outwardly. 1

4. A resistor as set forth in claim 1 wherein said sides are bent outwardly from the normal to said center memher and said channels are curved outwardly and said sides have edges portions bent outwardly.

5. A resistor as set forth in claim 1 wherein said sides are bent outwardly from the normal to said center member and said channels are bent inwardly.

6. A supporting clamp for fastening a U-shaped resistive ribbon member to an insulating mounting strip comprising two parallel spaced sides, a U-shaped member having a center panel and side legs, said member being inverted to space said center panel from the edges of said sides to recess said panel, said side legs and sides being joined to form rounded edges, means for securing said clamp to a mounting strip for embedding said rounded edges therein to prevent turning of said clamp and spacing said panel from said strip to form a circulating air passage therebetween and said sides extending on the other side of said center panel to form a recess for receiving a U-shaped resistive ribbon member fastened to said center panel.

7. A supporting clamp as set forth in claim 6 in which said edges have end projecting portions for embedding in a mounting strip.

8. A resistor of the ribbon type comprising a mounting strip having surfaces on opposite sides, a plurality of clamps each having spaced parallel sides extending normal to the strip and a center portion positioned between said sides to connect said sides together, fastening means extending through each of said center portion and said i strip from one side to the other to firmly draw said sides' against said insulating strip to prevent twisting of said clamp, a resistor ribbon formed in a plurality of aligned loops With parallel first sections fastened to said clamping means in a planar alignment, curved parts successively connecting sections on alternate sides to form a continuous resistive ribbon, said sections comprising an inter mediate longitudinally extending member and two sides extending normal to said member from opposite longitudinal edges, said sides having longitudinally extending channels cooperating with the channel formed by said sides and intermediate member to stiflly retain said sections in spaced relation to adjacent sections under conditions of forced circulation and vibration.

References Cited in the file of this patent UNITED STATES PATENTS 1,226,627 Barnum "1:--- May 22, 1917 1,373,689 Waller Apr. 5, 1921 1,680,201 Bihl et al Aug. 7, 1928 

